Pilot study comparing the neurologic and developmental outcome of two strategies of pH management (alpha stat vs. pH stat) during the cooling phase of cardio-pulmonary bypass, prior to circulatory arrest or low- flow, in infants and children undergoing reparative open heart surgery. Goals will be pursued in a prospective, randomized, single-center trial using homogenous populations of infants with simple ventricular septal defect, tetralogy of Fallot (without a history of spells), d- transposition of the great arteries, with intact ventricular septum or with ventricular septal defect.